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1. Field of the Invention
The present invention relates to the manufacture of lamps, and in particular to a hybrid sealing technique that enhances productivity when manufacturing the lamps.
2. Background Art
When manufacturing lamps, two electrodes are typically sealed within a lamp body to form a sealed enclosure where light is produced. Two methods are typically used to seal the enclosure. A first method is a pinch seal. A second method is a shrink seal. Shrink seals are superior to pinch seals, but it is difficult to position the electrodes and to secure them in place when performing a shrink seal.
Typical Lamp Configuration
A typical lamp configuration is shown in FIG. 1 where lamp body 5 contains a first electrode 15 and a second electrode 20 which are located opposite one another and which are respectively connected to a molybdenum foil part 25 and a molybdenum foil part 30. The connections between first electrode 15 and second electrode 20 and foil parts 25 and 30 are maintained by inner junction 80 and inner junction 85 within hermetically sealed portions 45 and 50 respectively. In addition, molybdenum wires 55 and 60 are connected to foil parts 25 and 30 by outer junctions 90 and 95.
Pinch Seal
To form a pinch seal, the lamp body 5, which may be comprised of quartz glass or other suitable material, is heated. When heated, the lamp body 5 becomes malleable. Pressure is applied in the area of foil parts 25 and 30 to pinch the malleable glass to the foil parts which creates a vacuum tight seal where junctions 35 and 90 are sealed at the same time. Pinch seals are disadvantageous because it is essential to not only seal the lamp but to also clean all impurities from the inside of the lamp before sealing it. Pinch seals offer no mechanism to effectively clean the sealed inside portion of the lamp. In addition, the pinch seal causes a large amount of pressure to the lamp body and electrode assemblies and the seal is often non-uniform which can lead to premature lamp failures and limits the pressure the lamps can be operated with.
Shrink Seal
To form a shrink seal, the unsealed lamp body is placed in a vacuum as shown in FIG. 2. To perform a shrink seal, the glass lamp body 200 is heated and a vacuum pumps pressure in opposing directions 210 and 220 which cause the lamp body to shrink and seal around foil parts 230 and 240. Shrink seals are beneficial because the vacuum pressure that pulls air from the inside of the lamp body also pulls impurities from the lamp body as well. Moreover, this type of seal is advantageous since a better glass uniformity around junctions 35 and 40 can be achieved. This leads to better reliability and better maintenance. When performing a shrink seal, it is crucial to position the electrode and to secure the electrode assembly in place.
To position and hold the electrode assembly in place while performing a shrink seal is an expensive and difficult process because a machine must be used to hold the electrode assemblies at the molybdenum wire portions 55 and 60 and to adjust the position of the molybdenum wires 55 and 60 so that the entire electrode assembly is positioned exactly in the right position when the shrink seal is achieved. In addition, the positioning of the electrode assembly must occur in vacuum conditions which makes the process even more difficult.
The present invention is a hybrid sealing technique. According to one or more embodiments of the present invention, an unsealed lamp body is heated and a partial pinch seal is performed on one side of the lamp body at an outer junction area. Then, a shrink seal is applied to that portion of the lamp body to completely seal the electrode within the lamp body by sealing an inner junction area.
In one embodiment, Nitrogen is flushed through the unsealed lamp body from the bottom of the lamp and over the electrodes to avoid oxidation and clean the lamp. In other embodiments, an inert gas like Argon, Neon, or other suitable gas is used. Then, the glass is heated and a partial pinch seal is performed at the bottom portion of the lamp only around an outer junction area. After that, a vacuum at the top of the lamp body pulls air out. Thereafter the glass is allowed to cool for a short time, 5 seconds for instance. Then, a burner is turned on and moved up the length of the area to be sealed (near the partially pinch sealed area) and in conjunction with the vacuum this causes the glass to soften and a shrink seal is achieved around an inner junction area.
The present invention retains the benefits of the shrink seal, but alleviates the difficulty associated with holding the electrode assemblies in place when performing a traditional shrink seal in vacuum conditions. In addition, the machine which holds the electrode assemblies in place is greatly simplified since the partial pinch seal holds the electrode in place while the shrink seal is occurring.